This application claims the priority of Austrian Patent Application, Serial No. 484/2000, filed Mar. 22, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates to a tunnel kiln useful for vertically perforated bricks.
Tunnel kiln are known in which unfired or green bricks are placed in raster-like spaced-apart relation on a transport device for travel through the heated furnace chamber of the kiln such that the vertical or slot perforations of all bricks are oriented in a common direction. Heating of the furnace chamber is implemented by tubular burners which are defined by longitudinal axes extending substantially in vertical direction.
Such kilns are normally configured in two designs: Some conventional kilns use a small number of burners which produce a high heat output. These burners generate temperatures at a degree that is unsuitable for direct exposure of the green bricks. Therefore, the burners are positioned at a distance to the green bricks and so aligned that the produced hot gases reach the green bricks only indirectly. Other kilns use a plurality of small burners which are typically secured in the roof of the kiln, whereby each burner generates only a small heat output.
Although the burners used in these conventional kilns are capable to produce sufficient temperatures, their efficiency of the firing action is not satisfactory because heat does not sufficiently circulate around and through the green bricks. Large, energy-rich burners permit only an indirect and untargeted heat circulation of the green bricks so that a significant flow through the brick perforations cannot be established. Small burners generate only a relative slow circulation which is incapable to fully penetrate through the bricks, in particular high-volume green bricks, even when directly targeted at the green bricks.
It is thus an object of the present invention to provide an improved tunnel kiln, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved tunnel kiln which realizes an significantly more efficient burning action.
It is another object of the present invention to provide an improved burner for use in a tunnel kiln according to the present invention.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a plurality of tubular burners for heating a furnace chamber, with the burners defined by longitudinal axes which extend essentially in a vertical direction; and a transport device for so transporting green bricks in raster-like spaced-apart relationship in a travel direction through the furnace chamber that the perforations of the green bricks are oriented in a common direction, wherein each of the burners has a nozzle body formed with orifices for combustion gases and positioned within a spacing between confronting end faces of neighboring green bricks, with the orifices of the nozzle body defined by longitudinal axes which extend substantially in a direction of the perforations of the green bricks.
Through the structure and disposition of the burner nozzle body with multiple orifices, the hot gas streams, produced by the burners, are mainly jetted out directly into the slot perforations of the green bricks so that the perforations are intensely penetrated by hot gases. Thus, all surfaces, in particular those areas of the perforations that have been neglected by conventional kilns, are exposed to intense hot gas streams. As a consequence, the green bricks are completely burnt after a relatively short time so as to establish a particularly economical procedure.
According to another feature of the present invention, the nozzle body has two groups of such orifices, whereby the orifices of each group is arranged along a line, with the groups of orifices being offset to one another by 180xc2x0. In this way, a burner is capable to burn two rows of green bricks simultaneously with hot gases, so that the total number of burners can be reduced, without adversely affecting the efficiency of the burning process. Suitably, the perforations of all green bricks extend transversely to the travel direction. Thus, there is no need to move the burners along their longitudinal axes. Rather the burners can be fixedly mounted immobile in a simple manner to the ceiling or roof of the furnace chamber.
According to another feature of the present invention, the burners are configured as high-speed burners. High-speed burners produce hot gases at particularly great flow speeds. At such speeds, ambient air is entrained so that the volume of the gas flow produced by the burner is significantly increased. This entrainment of air permits the operation of the burner with a relatively small flame and thus in a very energy-efficient manner, while still producing an intense hot gas stream, Suitably, the burners may have a core flow speed of 30 to 60 m/s, preferably 40 to 50 m/s. At such speeds, the ratio of fuel supplied to the burners and burning energy introduced into the green bricks is optimized.
According to yet another feature of the present invention, each of the burners has an outer tube formed with the orifices and closed at its lower end in the area of the nozzle body, an inner tube received in the outer tube and having a lower end disposed above the nozzle body, and a disk-shaped mixer closing the lower end of the inner tube. This configuration of the burners is less prone to malfunction, and ensures a discharge of combustion gases from all orifices at same speeds, so that the green bricks are evenly burnt across their entire height.